Determining the primary function of the finished component will direct you to a group of materials. For example, crystalline materials (i.e., nylon, acetal) outperform amorphous materials (i.e., polysulfone,Duratron® PEI or polycarbonate) in bearing and wear applications. Within the material groups, you can further reduce your choices by knowing what additives are best suited to your application.

Once you have determined the nature of the application (B&W or Structural), you can further reduce your material choices by determining the application's mechanical property requirements. For bearing and wear applications, the first consideration is wear performance expressed in PV and"k" -factor. Calculate the PV (pressure (psi) x velocity (fpm)) required. Using Figure 1, select materials whose limiting PV's are above the PV you have calculated for the application. Further selection can be made by noting the "k" wear factor of your material choices. In general the lower the "k" factor, the longer the wear life of the material.

Structural components are commonly designed for maximum continuous operating stresses equal to 25% of their ultimate strength at a specific temperature. This guideline is meant to compensate for the viscoelastic behavior of plastics that result in creep. Isometric stress-time curves are provided here to help you characterize a material's strength behavior as a function of time at both room temperature (Figure 2) and at 300°F (Figure 3).

Consider the thermal requirements of your application using both typical and extreme conditions.

A material's heat resistance is characterized by both its heat deflection temperature (HDT) and continuous service temperature. HDT is an indication of a material's softening temperature and is generally accepted as a maximum temperature limit for moderately to highly stressed, unconstrained components. Continuous service temperature is generally reported as the temperature above which significant, permanent physical property degradation occurs after long term exposure. This guideline is not to be confused with continuous operation or use temperatures reported by regulatory agencies such as Underwriters Laboratories UL.

The melting point of crystalline materials and glass transition temperature of amorphous materials are the short-term temperature extremes to which form stability is maintained. For most engineering plastic materials, using them at or above these temperatures should be avoided.

Consider chemicals to which the material will be exposed during use and cleaning.

Quadrant provides chemical compatibility information as a guideline in this brochure although it can be difficult to predict since concentration, temperature, time and stress each have a role in defining suitability for use. Nylon, acetal and Ertalyte® PET-P are generally suitable for industrial environments. Crystalline high performance materials such as Fluorosint® filled PTFE, Techtron® PPS and Ketron™ PEEK are more suitable for aggressive chemical environments (See Figure 5). We strongly recommend that you test under end-use conditions. Specific chemical resistance can be found on the property comparison chart.

Before proceeding to steps 5-7 it may be appropriate to consider additional material characteristics including:

Engineering plastics can expand and contract with temperature changes 10 to 15 times more than many metals including steel. The coefficient of linear thermal expansion (CLTE) is used to estimate the expansion rate for engineering plastic materials. CLTE is reported both as a function of temperature and as an average value. Figure 6 shows how many different engineering plastics react to increased temperature.

Modulus of elasticity and water absorption also contribute to the dimensional stability of a material. Be sure to consider the effects of humidity and steam.

Agencies such as the Food and Drug Administration (FDA), U.S. Department of Agriculture (USDA), Underwriters Laboratory (UL), 3A-Diary Association and American Bureau of Shipping (ABS) commonly approve or set specific guidelines for material usage within their industrial segments.

Select the most cost-effective shape for your part.

Quadrant offers designers the broadest size and configuration availability. Be sure to investigate all of the shape possibilities — you can reduce your fabrication costs by obtaining the most economical shape.

Consider Quadrant's many processing alternatives.

For:

Choose:

Long lengths Small diameters

Rod, plate, strip, profiles, tubular bar, bushing stock

Extrusion

Large stock shapes Near net shapes

Rod, plate, tubular bar, near, net configurations

Casting

Small Shapes in advanced engineering materials

Rod, disc, plate, tubular bar

Compression Molding

Small shapes in advanced engineering materials Small diameters

Rod, disc, plate, tubular bar

Injection Molding

Note: From process to process, many material choices remain the same. However, there are physical property differences based upon the processing technique used to make the shape.

Compression molded products are isotropic — they exhibit equal properties in all directions.

Determine the machinability of your material options.

Machinability can also be a material selection criterion. All of the Quadrant products in this site are stress relieved to enhance machinability. In general, glass and carbon reinforced grades are considerably more abrasive on tooling and are more notch sensitive during machining than unfilled grades. Reinforced grades are commonly more stable during machining.

Because of their extreme hardness, imidized materials (i.e., Duratron® PAI, Duratron® PI and Duratron® PBI) can be challenging to fabricate. Carbide and polycrystalline diamond tools should be used during machining of these materials. To aid you in assessing machinability, a relative rating for each material can be found on the property comparison charts.

Make sure you receive what you specify.

The properties listed in this site are for Quadrant EPP's materials only. Be sure you are not purchasing an inferior product. Request product certifications when you order.

Engineering Notes:

All material have inherent limitations that must be considered when designing parts. To make limitations clear, each material profiled in this site has an Engineering Notes section dedicated to identifying these attributes.